I've had a good think about it and the only way I'll try again is with some glue that dries rigid but not brittle like CA.

With any combination of double sided tape and shrink wrap there is too much chance of the lipo slipping and causing an unbalanced tail. Or worse, ejecting completely. Looking at the pics you can clearly see the shrink wrap barely covered the south end of the lipo cells.

For now I plan to wait for something better. Plonking down $70 for off the shelf tail blades that look dim compared to my DIY main blades doesnt make sense.

No, the ones from powerstream are much thinner, and off the top of my head I think they had too large a footprint for tail blades.

I'm considering trying again with the 550 and using epoxy and shrink tube to secure the lipos. But I'm going to wait until I have a very accurate digital scale since balance is critical on tail blades.

Thanks for the RR link, good find. No, havent tried button cells on tail blades. Seems like they would be heavier. I did fly the 550 with some DIY night paddles that had rechargeable li-ion 2016s or 2032s, I forget which. They made my cyclic a bit sluggish but it worked out ok.